Christine Swidorsky and Sean Stevenson had been planning to marry next year, but when they learned on July 26 that their son, Logan, had only a few weeks to live, they rushed to plan a wedding for the following week.

They plan to marry today in Jeannette, Pa., a suburb of Pittsburgh. Swidorsky will carry Logan, 2, down the aisle as she makes her way toward his dad to marry him after seven years together.

"We just said forget it," Stevenson told ABCNews.com. "Whether it's a small wedding or whatever, we were going to get married and have him in our wedding – have him in our family photos while he's still around."

Logan underwent chemotherapy and a cord blood transplant, and went into remission for nine months.

"As time went by, we started noticing Logan was doing really good." Stevenson said. "It kind of seemed like our family was getting back to some kind of normalcy."

But it didn't last. Swidorsky noticed Logan was acting strange, Stevenson said. He lifted his left arm a lot as if he were stretching, but she sensed there was something wrong with her son. They soon learned he had a tumor the size of an orange on his left kidney.

Doctors removed the tumor and the kidney, leaving Logan with a right kidney that was smaller than normal and didn't function properly, which is common in Fanconi's anemia patients. Further therapy to shrink the tumor wasn't possible, Stevenson said.

That was when doctors advised the family to make memories while they still could. They called the Make-a-Wish Foundation and set up a trip to Disney World (Disney World and ABC News are both owned by the Walt Disney Co.). On the second morning of their trip, Logan's grandmother woke Swidorsky and Stevenson.

"There's something wrong with Logan," she said.

Stevenson saw that Logan was lethargic and his eyes rolled toward the back of his head.

After stays at two hospitals in Florida, where doctors told the family that Logan was dehydrated and in septic shock, Logan was returned to Pittsburgh Children's Hospital on a medical flight. After spending almost three weeks on a ventilator, he woke up.

"He was home not even a week, maybe four or five days, and my fiance started noticing something," Stevenson said. "That's when they found a mass in the same spot where his left kidney would have been."

On July 26, doctors told Stevenson and Swidorsky that their son would live no more than three weeks.

"We were waiting for when Logan got better so it would be a wonderful day for him," Stevenson said of their previous wedding plans. "We just decided to have the wedding together this weekend and threw everything together in a week."

Logan doesn't talk much yet, but Stevenson said he knows something's wrong with him.

"If we're holding him and we're crying, he'll wipe our tears off, put his head down on our shoulders and pat our backs," he said. "He's a special, special little boy."

The family wants to share Logan's story to show the world how hard he fought, and to let other families with sick children know they're not alone.

"The toughest thing a parent has to do is bury one of their children," Stevenson said. "He showed me personally that I have to be as strong as he was."